Preparation of acids



Patented Dec. 18, 19 45 s v PATENT OFFICE PREPARATION or ACIDS Edward Payson Bartlett, Wilmington, Del., u-

sltnor to E. I. du Pont de Nemours 8: Company, Wilmington, Del., a corporation of Delaware No Drawing. Application September 25, 1942. Serial No. 459,740 Claims. (Cl. 260-541) to as involving hydrolysis. The process of this invention relates to the conversion of esters to acids with alcohols being incidentally prepared but, in contradistinction to saponiflcation, is directed specifically to the reaction or an organic ester with water in the presence or absence of an acid catalyst.

An object of the present invention is to provide an improved process for converting organic esters to their corresponding acids. Another object is to provide a process for carrying out such conversion under elevated pressures. A further object is to provide a process for the conversion of allphatic organic acid esters to corresponding organic acids and alcohols wherein the reaction is conducted under pressure and the products of the reaction are also separated under pressure. A further object is to provide a highly eflicient process for the preparation of acids and alcohols from esters which give azeotrope-forming esters and alcohols, the conversion of the ester and the separation of the acid and alcohol being conducted 1 under pressure. Other objects and advantages of the invention will hereinafter appear.

According to the invention, an organic ester is converted in the presence of water to its corresponding acid and alcohol by heating under pressure in the presence or absence or a hydrolysis catalyst and subsequently the alcohol formed and unreacted ester are distilled oil under. pressure,

leaving as a residue the desired acid. The alcohol, and ester are separated by known means and the latter returned to the conversion zone.

The eillciency of such a process is measured by the amount of alcohol removed; for every molecule or alcohol distilled over a molecule of acid is formed. Because of the change in azeotropic composition with pressure, pressure operation makes it possible to increase many told the alcohol removed and, as a consequence, thereby to increase the emciency of the process and greatly to increase the capacity of any given equipment. In addition to the aforesaid considerations, operating the conversion step under pressure increases the rate of reaction, the time required to reach optimum conversion being decreased from several hours to a matter of minutes. For instance, in the case of a mixture of methyl acetate and water, at 180 0., [the pressure is at 350 to 400 pounds per square inch and hydrolysis equilibrium is established in six minutes, whether or not an acid catalyst is present.

The conversion and the distillation of the alcohols therefrom are conducted in accord with the invention at pressures ranging between to 1000 pounds per square inch or more, the limiting factor on the high side being governed by the strength of the equipment used. The reaction should be conducted at substantially the boiling point 01' the reaction mixture under the pressure employed. For theconversion of methyl acetate to acetic acid, pressures ranging between 200 and 500 pounds per square inch, at corresponding temperatures ranging between 140 and 235 C. have been found to give especially eflicient operation.

The reaction may be further accelerated by the use oi a suitable hydrolysis catalyst such, for example, as hydrochloric acid, sulfuric acid, paratoluene sulfonic acid, boron trifluoride and its hydration and addition products and similar suitable hydrolysis catalysts. As has been stated, however. pressure considerably accelerates the rate of the reaction and, at higher pressures, in many instances, no catalysts are required, masmuch as the reaction rate is sufiiciently high in their absence. The reaction is conducted in the presence of water and there should be present at least two moles of water per mole of ester.

The process may be used for the preparation of acid from esters such, for example, as the methyl,

ethyl, normal and isopropyl, normal and isobutyl, amyl, hexyl, octyl, nonyl, dodecyl and higher straight and branch chain alcohol esters of formic, acetic, propionic, butyric, valeric, and the higher straight and branch chain aliphatic organic acids, as well as hydroxyacetic, lactic, acrylic, crotonic, oxalic, adipic, and highermono and polybasic aliphatic, organic acids as well as similar esters of the aromatic acids such as benzoic, toluic, etc.

Examples will now be given illustrating embodiments of the invention in which parts are by weight unless otherwise indicated.

Example 1.-A pressure still provided with a copper column packed with copper rings and fitted with a reflux head was charged with a 50% by weight aqueous methyl acetate solution containing 0.1% sulfuric acid. The packed column was equivalent to about six theoretical plates. Heat was applied and a pressure allowed to build up to approximately 400# per square inch, at which pressure the head temperature was approximately 180 C., and the pot temperature 210 C. Distillation was started without further processing and the following distillation data ob.- tained: 1

high methanol removal, atmospheric pressure operation in practice requires from 7 to 8 hours for the hydrolysis step, while during distillation the methanol content of the distillate averages 8-10%.

The emciency of the pressure system in this instance can of course be greatly increased over that demonstrated, if one employs a more effective column and a higher reflux ratio. The maximum efllciency would be accompanied by the production of an anhydrous binary of methanol and methyl acetate which at 400 lbs. has the composition: 58% methanol, 42% methyl acetate. This corresponds to 76% conversion of ester to acid and alcohol.

' I claim:

1. In a process of converting methyl acetate to acetic acid, the step which comprises has a [Pi-assure, 400 lbs. Reflux ratio, 5/1. Charge 1000 parts 01 water and 1000 parts of methyl acetate] Temperature Distillate Time out min. Head Pot Per Per Per Per 00 Parts cent cent cent cent MeOAc Hi0 HOAc MeOH 15 179 212 74. 8 84.0 19.1 0. 7 46.2 15 179 215 114. 6 58. 2 6. 7 0. 8 84. 8 15 180 218 85. 8 54. 5. 4 0- 0 80.0 180 221 78. 1 64. 0 5. 5 0.0 80. 5 15 181 224 66. 9 65. 0 5. 5 0. 0 29. 5 15 181 227 80. 9 66.0 5. 2 0.0 28. 1 15 182 231 60. 8 67. 2 6. 1 0. 0 26. 1 15 182 232 47. 7 68. 8 6. 8 0. 0 24. 7 15 180 232 47. 7 68. 7 6. 8 0. 0 2i. 5 1c 15 226 232 58. 9 70. 2 7. 6 0.0 22. 2 Pot residue-.. 1 300. 0 1. 79 a. 15

During the distillation about 45% of the ester Teens 5 Hydrolysis of methyl acetate lPressure, 400 lbs. Reflux ratio, 1/1.}

mixture of the methyl acetate and water under pressures between 200 and 500 pounds per square inch while separating the methanol by distillation under a similar pressure.

2. In a process of converting methyl acetate to acetic acid, the step which comprises boiling a mixture or the methyl acetate and water under pressures between 200 and 500 pounds per square inch while separating the methanol by distillation under a similar pressure.

3. In a process of converting methyl acetate Temperature Distillate Time, out min. Head Pot Per- Per Per Per Parts cent cent cent t MeOAc 3.0 B 050 MeOlI 1 15 179 212 61.7 49. 5 0.9 1.3 40.6 2.- 15 177 213 53. 1 51. 1 8. 9 0. 0 40. 0 3-. 15 135 216 26. 2 53. 5 10. 7 0. 0 35. 8 4.- 30 170 217 109. 1 58. 2 7. 5 0. 0 84. 3 5-. 15 171 2l9 32 2 60. 5 4. 4 0. 0 35. 1 6-. 15 172 221 41. 8 62. 4 3 1 0. 0 84. 5 7-- 15 179 224 57.7 629 5.0 0.0 82.1 8.- 15 170 227 104. 3 65. 9 5. 0 0. 0 28. 2 9- 15 170 229 29. 4 72. 4 8. 2 0. 0 19. 4 10. 15 178 229 2c 7 70. 6 8. 8 0. 0 20.5 11. 15 194 229 35. 3 71. 5 8. 5 0. 0 2o. 0 l2. 15 229 220 112.8 53. 9 25.8 2.2 18.1 13--- 15 229 229 95. 9 4. 2 80. 8 12. 0 1. 9 Pot residue--. l 220. 0 0. 78 62. 3 85. 3

In this case, of the ester was converted to acetic acid and methanol.

In Examples 1 and 2, the methanol distilled over ranged from a maximum of 46.2 to a minto acetic acid, the steps which comprise heat ing a 50:50 by weight mixture of methyl acetate and water containing approximately 0.1% sul- Iuric acid to a temperature between 179 and imum 01 18.1%. In contradistinction to this 226 C..atapressure of approximately 400 pounds 5. In a process of converting an ester of acetic acid selected from the group consisting of methyl acetate and ethyl acetate to acetic acid, the step which comprises heating a mixture of the ester of acetic acid and water under a pressure between 40 and 600 lbs. per. sq. 111., while separating by distillation the alcohol formed under a similar pressure.

v EDWARD PAYSON BARTLETT. 

